1. Field of the Invention
The present invention relates to a braking device for vehicles.
2. Description of Related Art
The braking device, as disclosed in Japanese Patent Laid-Open No. 2001-10481, uses a brake servo unit. The servo unit has the valve body of which a solenoid mechanism is incorporated. As the solenoid mechanism is energized, a movable core is moved to thereby open a valve mechanism such as an atmospheric pressure valve or a vacuum valve. This brake servo unit is operated by the displacement of an input rod working with a brake pedal. Furthermore the valve mechanism is able to operate the brake servo unit separately from operation of said brake pedal. Namely, as the solenoid is turned the power on and thereby the valve mechanism is operated, the quantity of air flowing between a constant pressure chamber and an operating pressure chamber of the brake servo unit is controlled, and a pressure difference between these chambers is generated. Thereby, it is able to provide a pressure with brake liquid in a master cylinder. The pressure thus increased is applied to a slave cylinder of each wheel, applying brakes to the vehicle. (Automatic brakes)
In the brake servo unit described above, in automatic brake application, in order to open the valve mechanism (atmospheric pressure valve) by moving the movable core of the solenoid mechanism, it is necessary to supply the solenoid current for generating a greater electromagnetic force than a total of three kinds of the following reactions: a reaction caused by the elastic deformation of an elastically deformable valve body forming the valve mechanism, a reaction caused by spring, and a reaction caused by the slide resistance of an elastically deformable seal member. Because the modulus of elasticity of the elastically deformable valve body and the slide resistance of the elastically deformable seal member vary with temperatures, the modulus of elasticity and the slide resistance increase at low temperatures (lower than xe2x88x9210xc2x0 C.) and decrease at high temperatures (higher than 60xc2x0 C.). Therefore, it is necessary to change the solenoid current for opening the valve mechanism according to high and low temperatures so that the solenoid current is increased at high temperatures and decreased at low temperatures.
On the other hand, in order to open the valve mechanism (vacuum valve) by moving the movable core of the solenoid mechanism for releasing the automatic brakes, it is necessary to supply the solenoid current for generating a greater electromagnetic force than a total of two kinds of the following reactions: a reaction caused by spring deformation and a reaction caused by the slide resistance of the elastically deformable seal member. As stated above, the slide resistance of the elastically deformable seal member vary with temperatures, so that it is necessary to change the solenoid current for opening the valve mechanism according to high and low temperatures. It is necessary that the solenoid current is increased at high temperatures and decreased at low temperatures.
The present invention solves the above-described problem by the following way. During pressure-increasing of master cylinder in automatic brakes, the solenoid current, at the time the valve mechanism for pressure-increasing is opened and the pressure is changed, is learned and recorded as learned value of pressure-increase starting current. Then, when the valve mechanism is opened again, the solenoid current is corrected on the basis of the learned value of pressure-increase starting current recorded above. The solenoid current necessary to open the valve mechanism is thereby supplied precisely without directly measuring the temperature.
During pressure-decreasing of master cylinder in automatic brakes, like during the pressure-increasing, the solenoid current, at the time the valve mechanism for pressure-decreasing, is opened and the pressure is changed, is learned and recorded as learned value of pressure-decrease starting current Then, when the valve mechanism is opened again, the solenoid current corrected on the basis of the learned value of pressure-decrease starting current recorded above.
It becomes possible to constantly supply the proper solenoid current to the brake servo unit by updating the learned value of pressure-increase starting current every time the pressure is increased, excepting the first time of pressure-increasing after starting the servo unit. This operation is similarly applicable in the case of pressure decreasing.
It is also possible to constantly supply the proper solenoid current to the brake servo unit by recording a solenoid current command as the learned value of pressure-increase starting current in place of the solenoid current. This operation is similarly applicable in the case of pressure-decreasing.